Production of artificial threads, films, and the like



Patented Mar. 24, 1953 PRODUCTION OF ARTIFICIAL THREADS, FILMS, AND THE LIKE Leslie A. Bashford and George Doubleday, Coventry, England, assignors to Courtaulds Limited, London, England, a British company No Drawing. Application May 11, 1951, Serial No. 225,915. 1948 Y 3 Claims.

This invention relates to the production of artificial threads, films and the like of secondary cellulose acetate by wet spinning, the term thread being used in a general sense to include threads, fibres, filaments, staple fibresand like filamentary materials. This application is a continuation-in-part application of our application No. 122,832, filed October 21, 1949.

Proposals have already been made for wet spinning cellulose acetate by spinning solutions of cellulose acetate into various coagulatin baths. Thus British patent specification No. 7,341 of 1903 describes a process in which solutions of acidyl cellulose, for example in acetic acid, phenol, chloroform or mixtures of solvents are spun through jets into a liquid such as alcohol, benzene or petroleum spirit. In British patent specification No. 3,973 of 1911 it is proposed to use aqueous liquids for the purpose of coagulating cellulose acetate solutions in wet spinning, water, aqueous solutions of bases or salts and aqueous'solutions of acetic acid being specifically mentioned. Subsequently, proposals for wet spinning cellulose acetate using coagulating baths were made and among the coagulating baths suggested may be mentioned; aqueous caustic soda solutions saturated with sodium chloride (British patent specification No. 13.872 of 1914); strong basic aqueous solutions such as sodium lye or ammonia (British patent specification No. 15,544 of 1914); aqueous baths containing ammonium thiocyanate or other thiocyanates (British patent specification No. 177,868); aqueous solutions of zinc chloride or other salts having a latent solvent power for cellulose acetate (British patent specification No. 179,234); aqueous sodium sulphate solutions (British patent specification No. 198,392); concentrated aqueous calcium chloride solutions (United States patent specification No. 1,551,791) for mixtures of nitrocellulose and cel lulose acetate; solutions of calcium nitrate or ammonium nitrate (United States patent specification No. 1,679,850); solutions of ammonium nitrate containing ammonium thiocyanate or zinc chloride (British patent specification No. 312,671); strong solutions of mineral acids or acid esters (United States patent specification No. 1,903,299); solutions of ammonium or alkaline earth metal nitrates (French patent specification No. 711,668) and aqueous solutions of ammonium salts such as ammonium chloride, ammonium sulphate and ammonium acetate, sodium chloride, sodium sulphate, sodium acetate and calcium chloride (United States patent specification No. 2,218,029)

In Great Britain November 24,

The object of the present invention is to provide an improved coagulating medium for wet spinning secondary cellulose acetate.

In accordance with the present invention, in a process for the production of artificial threads, films and the like of secondary cellulose acetate by extruding a solution of the cellulose acetate through a jet into an aqueouscoagulating bath containing at least one metal salt as the active coagulant medium, the cellulose acetate solution used is an aqueous acetic acid solution containing from about 9 to about 15 per cent by weight of cellulose acetate based on the weight of the solution and the coagulating bath employed contains free acetic acid and potassium acetate in a concentration of from 20 per cent by weight up to saturation point; solutions containing concentrations of the order of 40 per cent by weight of potassium acetate are particularly suitable.

The coagulating bath preferably contains acetic acid in a concentration within the range of from to 250 grams of acetic acid per litre of bath.

Cellulose acetate spinning solutions for use in this invention are those in aqueous acetic acid which are obtained by the normal acetylation process after ripening and neutralisation of the acid catalyst have been eiiected so that the steps of precipitating, washing and drying the cellu lose acetate in the form of flake are eliminated. The concentration of the solution is within the range of from 9 to 15 per cent by weight based on the weight of the solution. 1 The solution may be clear or pigmented.

In carrying out the process according to the invention the spinning solution is preferably heated to a temperature higher'than that of the coagulating bath as described for example in British patent specification No. 341,148; for example the spinning solutioncmay be heated to a temperature of about 40 to centigrade while the coagulating bath may be maintained at a temperature within the range of 15 to 45 centigrade, preferably 25 to 35; centigrade, for example about 30" centigrade.

When a solution of cellulose acetate in aqueous acetic acid is wet spun continuously in accordance with the invention, the concentration of acetic acid in the bath will increase under static conditions. It is therefore preferred to withdraw part of the bath liquor containing acetic acid at a higher concentration, to recover acetic acid from the withdrawn liquor, and to feed potassium acetate solution, containing acetic acid at a lower concentration to the bath in a continuous process so that spinning conditions are maintained substantially constant.

The present invention is particularly useful for making staple fibres by the process described and claimed in the specification of our co-pending application Serial No. 122,833, dated October 21, 1949.

The use of potassium acetate as a coagulant in accordance with the present invention permits the production of cellulose acetate threads having filament deniers as low as 1.5, mean fibre tenacities of at least 1.1 grams per denier, and dry extensibilities of 25 to 35 per cent or even 40 per cent in this respect potassium acetate shows a marked improvement over previously proposed coagulants such as sodium acetate. Cellulose acetate threads produced by wet spinning with previously known coagulating baths have also generally shown a marked tendency to stain with certain direct cotton dyestuffs thus restricting their possible use in the textile industry. Wet-spun threads obtained using coagulating baths containing potassium acetate in accordance with this invention are not markedly stained by direct cotton dyestuffs and in this respect are similar to the normal dry-spun threads. The threads obtained according to the invention also resist acid or wool dyes in a manner similar to dry spun threads. Films obtained according to the invention are in general clear and lustrous.

The threads coagulated in accordance with the invention after washing may be treated if desired with softening agents or lubricating agents; they may also be treated after drying with tinting agents or antistatic agents, for example by an atomised spray.

The invention is illustrated by the following examples in which the parts and percentages are by weight:

Example 1 A cellulose acetate solution in an acetic acidwater mixture was prepared as follows:

100 parts of cellulose in the form of cotton linters were pretreated for 5 hours with 40 parts of a 2 per cent solution of sulphuric acid in glacial acetic acid. The pretreated cellulose was then reacted in a mixer with a further 330 parts of glacial acetic acid, 14 parts of sulphuric acid, and 240 parts of acetic anhydride, the reaction temperature being kept below 40 centigrade by cooling the mixer. When the cellulose had reacted, namely after about 6 hours, 33 parts of water were added and the mixture allowed to ripen for about 36 hours at 26 centigrade. The catalyst was then neutralised by adding and mixing in 132 parts of a 19.8 per cent solution of sodium acetate in 50 per cent aqueous acetic acid and then a further 159 parts of acetic acid and 254 parts of water were added and mixed in. The solution obtained was filtered and deaerated under vacuum for 6 hours.

The spinning of the solution so obtained was efiected as follows:

The solution was heated to approximately 55 4 centrigrade and was extruded by a metering pump at a rate of 17.5 cubic centimetres per minute through a jet having 372 holes each of 0.002 of an inch diameter into an aqueous coagulating bath at 30 centigrade containing 40 per cent of potassium acetate and 50 grams of acetic acid per litre of solution. The filaments so formed were taken up on a godet at a speed of 23 metres per minute and were then passed to a second godet rotating at a speed designed to stretch the filaments 18 per cent. The filaments were then washed free from acid and salt, collected as a thread, and dried in a current of hot air.

A thread having a soft handle was obtained. Fibre tests on the thread gave the following results:

Denier 2.65

Tenacity (dry) grams/denier 1.34

Extensibility per cent 25.5

Example 2 The procedure described in Example 1 was repeated with the only exceptions that:

(a) 1.5 per cent of titanium dioxide, based on the weight of the cellulose acetate, was added as a dispersion to the spinning solution and (b) The concentration of acetic acid in the coagulating bath was 75 grams per litre.

A delustred thread having a soft handle was obtained. Fibre tests on the thread gave the following results:

Denier 2.5 Tenacity (dry) grams/denier 1.25 Extensibility per cent 34.5

Example 3 The cellulose acetate solution was the same as that used in Example 1.

The cellulose acetate solution heated to 55 centigrade was extruded by a pump at a rate of 200 cubic centimetres per minute through a jet having 3000 holes each of 0.002 of an inch in diameter into an aqueous coagulating bath at 30 centigrade containing approximately 40 per cent of potassium acetate and grams of acetic acid per litre of solution. The filaments so produced were withdrawn from the bath as a tow of substantially parallel filaments at a speed of 32 metres per minute and were continuously washed with water till free from acid and salt. The tow was then given a 16 per cent stretch in boiling water and dried.

Fibre tests on the product gave the following results:

Denier 2.4 Tenacity (dry) grams/dem'er 1.26 Extensibility per cent 32.5

Example 4 The cellulose acetate spinning solution was similar to that used in Example 2 with the only exception that the cellulose acetate concentration was reduced to 10.25 per cent. It was heated to 50 centigrade and. extruded by a metering pump at a rate of 116 cubic centimetres per minute through a jet having 2500 holes, each of 0.002 of an inch in diameter, into an aqueous coagulating bath at 30 centigrade containing approximately 40 per cent of potassium acetate and grams per litre of acetic acid. The filaments so produced were withdrawn from the bath as a tow of substantially parallel fibres at a speed of 32.4 metres per minute, continuously washed with water till free from acid and salt, then given an 8 per cent stretch in water at 90 Centigrade and dried.

Fibre tests on the product gave the following results:

Denier 1.53

Tenacity (dry) grams/denier- 1.36

Extensibility per cent 39.3

Example A cellulose acetate solution in an acetic acidwater mixture was prepared as described in Example 1 and was spun as follows:

The solution was heated to 30 centigrade and was extruded by a metering pump at a rate of 62 cubic centimetres per minute through a slit jet 1 inches long by 0.0025 of an inch wide into an aqueous coagulating bath at 33 to 35 centrigrade containing 40 per cent of potassium acetate and 120 grams of acetic acid-per litre of solution. The long axis: of the slit jet was arranged in the horizontal plane with the film issuing from the jet substantially horizontally. The resultant film was withdrawn from the bath after an immersion of 6 feet and passed at a films and the like of secondary cellulose acetate comprising extruding a direct acetylation solution consisting essentially of water, acetic acid, and from 9 to 15 per cent by weight of secondary cellulose acetate based on the weight of the solution, through a jet into an aqueous coagulating bath containing potassium acetate in a concentration of from 20 per cent by Weight up to saturation point as an active coagulating medium and also containing free acetic acid.

2. A process as claimed in claim 1 in which the coagulating bath contains free acetic acid in a concentration within the range of from 50 to 250 grams of acetic acid per litre.

3. A process for the production of threads, films and the like of secondary cellulose acetate comprising extruding a solution consisting of water, acetic acid, and from 9 to 15 per cent by weight of secondary cellulose acetate based on the weight of the solution, through a jet into an aqueous coagulating bath containing potassium acetate in a concentration of per cent by weight as an active coagulating medium and also containing free acetic acid in a concentration within the range of from to 250 grams of acetic acid per litre.

L. A. BASHFORD. GEO. DOUBLEDAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,147,641 Dickie et al Feb. 21, 1939 2,341,586 Alles Feb. 15, 1944 

1. A PROCESS FOR THE PRODUCTION OF THREADS, FILMS AND THE LIKE OF SECONDARY CELLULOSE ACETATE COMPRISING EXTRUDING A DIRECT ACETYLATION SOLUTION CONSISTING ESSENTIALLY OF WATER, ACETIC ACID, AND FROM 9 TO 15 PER CENT BY WEIGHT OF SECONDARY CELLULOSE ACETATE BASED ON THE WEIGHT OF THE SOLUTION, THROUGH A JET INTO AN AQUEOUS COAGULATING BATH CONTAINING POTASSIUM ACETATE IN A CONCENTRATION OF FROM 20 PER CENT BY WEIGHT UP TO SATURATION POINT AS AN ACTIVE COAGULATING MEDIUM AND ALSO CONTAINING FREE ACETIC ACID. 